U-values

Windows consist of glazing and framing. Both components contribute to the overall performance of the window, called a U-value. U-values measure the amount of heat passing through a glazed unit in watts; the lower the U-value, the more energy efficient your window is. In your home, you should aim to use windows with low U-values because they will be more effective at keeping out unwanted heat and cold. Low U-values can improve your comfort levels and reduce your energy costs.

Timber frames

Timber window frames are highly energy efficient as they do not conduct heat. They perform extremely well when combined with double glazing, but do require more maintenance than either aluminium or uPVC frames.

uPVC frames

Another efficient frame type used with double-glazed windows is uPVC, or un-plasticised Polyvinyl Chloride. uPVC frames have been used in Europe and the United States for many years, as they perform in a similar manner to timber frames but are more durable and require little maintenance.

Combination frames

Aluminium window frames that combine aluminium and timber are more efficient than thermally broken aluminium frames. These frames usually combine low maintenance aluminium as the external component and timber, which acts as an insulator, as the internal component of the frame.

Aluminium frames

Aluminium is a popular choice for window frames because it's light, strong and requires little maintenance. Unfortunately, it isn't the most energy efficient choice. Because aluminium is a good conductor, you can lose a great deal of heat through the frames in winter and gain unwanted heat in the same way during summer. This could impact the comfort of your home, the cost of your energy bills and the overall performance of double-glazed windows.

To reduce heat loss during winter and heat gain during summer through aluminium window frames, be sure to install a thermal break. A thermal break is an insulating material placed between the interior and the exterior elements of the window frame, which will minimise the transfer of heat and cold through the frame.

Questions to ask your window supplier

Your window supplier or installer can provide valuable ideas and industry knowledge, but it is important that you ask the right questions.

Window Energy Rating Scheme

The Window Energy Rating Scheme (WERS) gives a star rating to a window's glazing and frame energy performance, making it easier to compare different windows and decide which is best for your needs.